Nine-eleven Museum officials revealed new details of the plans for the space last week and acknowledged it will not be an easy event to explain without offending someone.

Joe Daniels, president of the National September 11 Memorial & Museum, said deciding exactly what to say about the hijackers was one of the “tough issues we are grappling with.”

When Daniels was asked by a reporter if alternative 9/11 views such as the attack being prompted by U.S. bases in Saudi Arabia will be presented, Daniels said the museum’s inclination was to “let the perpetrators speak for themselves” by using their “martyrdom tapes.”

In response to a follow-up question, Daniels said the museum will not portray the killers as martyrs. “No one will come to this museum and leave with a feeling of heroism for the people who committed the crimes that we bear witness to today,” he said.

The museum is not planning to make the videos of the hijackers available but is considering making portions of the video transcripts part of the exhibit.

Describing 9/11 as the most documented event in history, museum officials do plan to make ample use of all of the videos, audio files and photos connected to 9/11. They announced last week that people all over the world were welcome to submit stories and documents to 911history.org to become part of the museum’s permanent collection. The site makes use of Google Maps to help put the submissions in context.

The museum also released new images of the 121,000-square-foot underground museum last week. Visitors will descend under the memorial plaza to view the exhibits and remnants from 9/11 and its aftemath including the W.T.C.’s bedrock and slurry wall, and the Survivors’ Stairway, which some 9/11 survivors used to leave the W.T.C. Some of these elements were originally thought to be part of the memorial but they have become part of the museum. If the museum is able to avoid charging an admission, the distinction probably will not matter, but if it does charge, it will mean that artifacts that some consider part of the public memorial will have an admission fee.

Daniels said the museum foundation continues to look for ways to make it free.

Pieces of the original W.T.C. facade will be visible from the memorial plaza. Under the current schedule, the plaza would open by Septmeber 2011, and the museum one year later, although some construction anylysts have concluded the timeline goals are unrealistic given the complexities of building the new W.T.C.